Reciprocating piston machine

ABSTRACT

A reciprocating piston machine, in particular a compressor, such as for the air conditioning system of an automotive vehicle. The machine includes a casing and at least one casing cover. A working unit including pistons and is arranged or formed in the casing. The intake and exhaust zone or a front shaft bearing are arranged or formed in the casing cover (covers). The casing cover is screwed on the casing. The screw assembling is carried out with the aid of ring nuts or saw tooth screw threads between the casing and the casing cover, wherein the casing and cover are made of materials with different strengths and different thermal expansion coefficients.

The present invention is directed to a reciprocating piston machine, inparticular a compressor, preferably for the air conditioning system of amotor vehicle, having a housing and at least one housing cover, thepower unit encompassing the pistons being accommodated or formed in thehousing, and the suction and discharge areas or a forward shaft bearingbeing accommodated or formed in the housing cover, and the housing coverbeing screw-coupled to the housing.

BACKGROUND

Reciprocating piston-type machines of the type described are generallyknown. In this context, it may be a question of a compressor, thus, forexample, of a compressor for the air conditioning system of a motorvehicle. Compressors of this kind are usually referred to asair-conditioner compressors, and include a housing, which encompasses anexternally driven compressor unit or pump unit. The compressor unitdesigned, for example, as an axial piston machine, includes, in turn, atleast one piston which is able to reciprocate in a cylinder block. It iscustomary for a compressor of this kind to be equipped with a pluralityof pistons, which are reciprocated in the direction of theirlongitudinal axis in response to the rotation of a supporting plate overa swash plate or in response to the pivoting of a pivot plate or a pivotring, in the case of a swash plate, the swash plate being mounted in atorsionally fixed manner in the housing. The housing is typically sealedby at least one housing cover which is screw-coupled to the housing, forexample. In this context, the form of a ring nut that functions betweenthe housing and the housing cover, or of a single thread or of aseparate threaded ring can be used for the screw connection.

In the case of air-conditioner compressors having screwed-in,pressurized back covers, covers or cylinder heads, high axial forces aretransmitted via the thread into the housing. In conjunction with thetriangular threads (i.e. V-threads) typically used, these axial forcesproduce a radial pressure which is exerted via the thread on thehousing. This radial pressure on the housing leads to relatively highperipheral stresses in the housing and increases the friction torqueduring the screw-in operation. Moreover, additional thermal stresses aresuperposed on these forces during operation and at standstill.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a compressor whichwill not have these disadvantages.

The present invention provides a reciprocating piston-type machine thatincludes a housing; a housing cover; a power unit disposed in thehousing and including a plurality of pistons; one of a suction anddischarge area and a forward shaft bearing disposed in the housingcover; and a screw connection configured to screw-couple the housingcover to the housing, the screw connection including sawtooth threadbetween the housing and the housing cover. In accordance with thesefeatures, the already realized related-art screw connection has a veryparticular design, namely the form of a so-called sawtooth thread.

It was discovered in accordance with the present invention that, asbefore, it is still possible to screw-couple the housing and the housingcover, but the problems associated with the related art methods may beminimized by using a sawtooth thread.

A reciprocating piston-type machine is preferred in which the peripheralor equivalent stresses caused by the sawtooth thread in the housing wall(and also in the cover and, respectively, the threaded ring) in theradial direction in response to axial compressive load on the cover, aresubstantially reduced in comparison to a triangular thread or similarthreads.

In addition, a reciprocating piston-type machine is preferred, in whichthe tightening torque is substantially reduced by the sawtooth thread incomparison to a triangular thread or similar threads.

A reciprocating piston-type machine is also preferred, in which thethermal stresses are reduced by the sawtooth thread, i.e., theprestressing is maintained as compared to a triangular thread or similarthreads.

A reciprocating piston-type machine has the distinguishing feature thatthe sawtooth form of the structural component having a substantiallylower material strength (cylinder head of aluminum, for example) issubstantially wider/larger than the sawtooth form of the structuralcomponent having a substantially higher material strength (housing ofsteel, for example). Here as well, a reciprocating piston-type machineis preferred, in which the length of this thread is substantiallyreduced as compared to the normal sawtooth thread. The result is shorterproduction times. A reciprocating piston-type machine is likewisepreferred in which the thread has a substantially steeper pitch thandoes a standard sawtooth thread, without the height of the thread toothbeing increased.

A reciprocating piston-type machine is also preferred in which thethread renders possible substantially less precise manufacturingtolerances does a standard sawtooth thread. A reciprocating piston-typemachine is likewise preferred in which the wider sawtooth form is sowide that the thread may also be used as a surface for clamping duringfurther machining of the particular component.

A reciprocating piston-type machine is also preferred, in which theflank angle of the sawtooth thread is <0° instead of the standard 3°according to DIN 515, when the component(s) having the external thread(“bolt”) are made of a material having a greater thermal expansion (forexample aluminum) than the component(s) having an internal thread(“nut”, for example steel). As used herein, thermal expansion is usedsynonymously with thermal expansion coefficient.

In addition, a reciprocating piston-type machine is preferred, in whichthe flank angle of the sawtooth thread is >0° when the component(s)having the external thread are made of a material having a smallerthermal expansion than the component(s) having an internal thread.

The present invention is described below in greater detail withreference to the figures, which show:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 an air-conditioner compressor having a thread on the cylinderhead;

FIG. 2 the front section of a compressor having a thread on the frontcover;

FIG. 3 the representation of a triangular thread;

FIG. 4 the representation of a sawtooth thread;

FIG. 5 the representation of a special sawtooth thread having a broadand narrow toothing;

FIG. 6 the representation of components having different thermalexpansion.

DETAILED DESCRIPTION

The housing of an air-conditioner compressor and several of itscomponent parts are shown in cross section in FIG. 1. In a housing 1,which is preferably manufactured from steel or materials having similarstrength properties, a piston and crankshaft assembly having a cylinderblock 2 is accommodated, in which reciprocating pistons 3 suction andcompress refrigerant, and discharge it again under pressure. Pistons 3are coupled via piston shoes 4 to a drive device in the form of a pivotplate or a pivot ring 5. Pivot ring 5 is set into rotation by a driveshaft 6 via a driver (not shown). Pivot ring 5 may assume variouspivoting angle positions and thus vary the piston displacement of thecompressor. Drive shaft 6 is driven via a belt pulley device 7 in thebelt drive of a combustion engine, as is customary for air-conditionercompressors used in motor vehicles.

Above cylinder block 2, a valve plate 8 having suction and dischargevalves (not shown in detail here) is accommodated inside housing 1,piston 3 suctioning refrigerant out of an air-conditioning system from asuction chamber 10 via suction valves and suction orifices 9 and,following a certain rotation, compressing the refrigerant insidecylinder block 2 and delivering it via discharge orifices 11 and thedischarge valves into pressure chamber 12. From there, the refrigerantis transferred, inter alia, into the air-conditioning system. By way ofcontrol valves 13, which are accommodated in the cylinder head region ofthe compressor, high pressure may be admitted from pressurized region 12into the compression chamber, and the level of the compression chamberpressure may be regulated down, in turn, by admitting pressure intolow-pressure region 10. The pivoting angle of the piston and crankshaftassembly and thus the piston displacement then automatically adjustsitself based on the level of the corresponding compression chamberpressure. Configured between housing 1, which, as already mentioned, inthe case of CO₂ compressors, due to the high pressure, may preferably bemanufactured from steel or similar high-strength materials, and cylinderhead 15, which may be manufactured from an aluminum alloy, is a threadedconnection 14. The entire cylinder head may be assembled anddisassembled via this one thread. In this context, when working with therefrigerant CO₂, high pressures of up to 160 bar, as well astemperatures of up to 130° Celsius cause stresses to occur within themachine which, depending on the thread structure, manifest themselves asradial and axial stresses. The difference in the thermal expansion ofthe housing materials such as steel or the like, and of the cylinderhead materials, such as aluminum, may pose an additional problem.

FIG. 2 illustrates the housing part of another compressor, in which thefront housing part is also sealed by a cover. The substantially tubularhousing 20 made of steel or similar materials is screw-coupled via athread 22 to front housing cover 21. A shaft bearing (not shown here),as well as a shaft sealing device may be accommodated in the area of thefront housing cover. Front housing cover may likewise be made of a steelmaterial or also of an aluminum alloy. At some locations, the fronthousing cover includes fastening devices in the form of fixing eyelets23, which, via cutouts 24, enable the compressor to be secured tocorresponding mounts of the automotive engine. This thread 22 in thefront area of the compressor is also subjected to corresponding stressesdue to compression chamber pressures and temperature loading, even ifthey are not as high as on the cylinder head side, where, for example,in FIG. 1, in pressurized region 12, the high pressure acts on cylinderhead 15 and attempts to press it away toward the outside.

A normal triangular thread, which is mainly provided for these kinds offastenings, is illustrated in FIG. 3. In accordance with thread angle 30of approximately 60°, due to axially acting pressures on the cylinderhead, for example, the axial forces are applied via the angles of thethread into the housing and produce axial and radial stresses there.

FIG. 4 depicts a sawtooth thread which is principally used by experts inthe field for transmitting forces through screw drive mechanisms in onlyone axial direction, for example in impact screw presses. In accordancewith the present invention, this sawtooth thread is also particularlyadvantageous for fastening the compressor parts described above. Byusing a sawtooth thread of this kind, it is possible to reduce both thethread engagement torque during assembly, as well as the radial pressureacting on the housing during operation of the compressor and thus theequivalent stresses in the thread region of the housing. Due to thereduction in loading on the housing and in the tightening torque, giventhe same outlay for manufacturing, smaller wall thicknesses in thehousing and shorter threads are possible. Associated with this is aweight reduction, as well.

Another design according to the present invention of a sawtooth threadfor air-conditioner compressor applications is illustrated in FIG. 5.

In FIG. 5, the sawtooth thread in question of housing 51, which is madeof the previously described steel material, is provided with suitablynarrow thread teeth 50, while cylinder head 52 made of an aluminum alloyis provided with wide thread teeth 53 suitably designed in accordancewith the low strength of the aluminum material. This means that, inorder to better utilize the materials in the housing thread, a standardsawtooth thread is appropriately modified in accordance with the presentinvention. This modification leads to a steeper thread pitch and to areduced thread length, thereby resulting in shorter thread fabricationtimes. Also, less precise tolerances are possible, such as those atclearance (a), for example. Another advantage may also be derived inthat, due to large tooth width 54, the external thread of the cylinderhead may be utilized for clamping purposes in the further machining ofthe cylinder head. The sawtooth thread is aligned in such a way that,for example, the compression chamber pressure, a well as the highpressure within the cylinder head act from direction 55 on the cylinderhead and thereby press the perpendicular flanks of the cylinder headthread and of the housing thread against each other. As a result, theaxial compressive forces are also principally transmitted in the axialdirection, and the radial components are minimal in comparison to atriangular thread, as illustrated in FIG. 3.

FIG. 6 depicts components of materials having different thermalexpansion. Component 60 represents the housing, for example, whilecomponent 64, for example, a part of the cylinder block, and component62 may represent the cylinder head or the housing cover of thecompressor. Component 62 and component 60 are interconnected by asawtooth thread 66 in accordance with the present invention, while acentering of components 64 and 62 within component 60 is shown in region68. If, at this point, components 62 and 64 have a greater thermalexpansion than component 60, then a sawtooth thread having a flank angleof <0° is selected instead of the flank angle of 3° in accordance withDIN 515. Then, in the case of a heating or cooling, and given availableexpansion space in the thread root for the engaging thread tooth, thereis no change in the prestressing when the direction of the thread flankruns in parallel to the occurring thermal expansions in the axial andradial direction of component 64 and of component 62 minus the thermalexpansions of component 60.

When components 62 and 64 have a smaller thermal expansion thancomponent 60, then a sawtooth thread having a flank angle of >0° isselected. Then, in the case of a heating or cooling, and given availableexpansion space in the thread root for the engaging thread tooth, thereis no change in the prestressing when the direction of the thread flankruns in parallel to the occurring thermal expansions in the axial andradial direction of component 64 and of component 62 minus the thermalexpansions of component 60.

Thus, in accordance with the present invention, the standard flank angleof the sawtooth thread of 3° according to DIN 515 is selectively reducedas a function of the thermal expansion of the materials used and of thegeometry of the components. This has the advantage that the thermalstresses in the thread region are able to be further reduced and,respectively, the prestressing in the thread region is able to bemaintained. Further advantages are derived in that there is less loadingon the housing, given the same outlay for manufacturing. As a result,smaller wall thicknesses in the housing and shorter threads arepossible. Associated with this is a weight reduction, as well.

The claims filed with the application are proposed formulations and donot prejudice the attainment of further patent protection. The applicantreserves the right to claim still other combinations of features that,so far, have only been disclosed in the specification and/or thedrawings.

The antecedents used in the dependent claims refer, by the features ofthe respective dependent claim, to a further embodiment of the subjectmatter of the main claim; they are not to be understood as renouncingattainment of an independent protection of subject matter for thecombinations of features of the dependent claims having the main claimas antecedent reference.

Since, in view of the related art on the priority date, the subjectmatters of the dependent claims may form separate and independentinventions, the applicant reserves the right to make them the subjectmatter of independent claims or of divisional applications. In addition,they may also include independent inventions, whose creation isindependent of the subject matters of the preceding dependent claims.

The exemplary embodiments are not to be understood as limiting the scopeof the invention. Rather, within the framework of the presentdisclosure, numerous revisions and modifications are possible, inparticular such variants, elements and combinations and/or materials,which, for example, by combining or altering individual features orelements or method steps described in connection with the generaldescription and specific embodiments, as well as the claims, andcontained in the drawings, may be inferred by one skilled in the artwith regard to achieving the objective, and lead, through combinablefeatures, to a new subject matter or to new method steps or sequences ofmethod steps, also to the extent that they relate to manufacturing,testing, and operating methods.

1. A reciprocating piston-type machine, comprising: a housing; a housingcover; a power unit disposed in the housing and including a plurality ofpistons; one of a suction and discharge area and a forward shaft bearingdisposed in the housing cover; and a screw connection configured toscrew-couple the housing cover to the housing, the screw connectionincluding sawtooth thread between the housing and the housing cover;wherein the screw connection includes first thread side including afirst material having a first material strength and a second thread sideincluding a second material having a second material strength higherthan the first material strength, wherein each tooth of the first threadside is larger than a corresponding tooth of the second thread side. 2.The reciprocating piston-type machine as recited in claim 1, wherein alength of the sawtooth thread in an axial direction is less than astandard sawtooth thread.
 3. The reciprocating piston-type machine asrecited in claim 1, wherein a pitch of the saw tooth thread is steeperpitch than a standard sawtooth thread.
 4. The reciprocating piston-typemachine as recited in claim 1, wherein a manufacturing tolerance of thesaw tooth thread is larger than a standard manufacturing tolerance of astandard sawtooth thread.
 5. The reciprocating piston-type machine asrecited in claim 1, wherein the first thread side is disposed on one ofthe housing and the housing cover, and wherein each tooth of the firstthread side includes an upper surface that is sufficiently wide forclamping during further machining of the housing or housing cover.
 6. Areciprocating piston-type machine, comprising: a housing; a housingcover; a power unit disposed in the housing and including a plurality ofpistons; one of a suction and discharge area and a forward shaft bearingdisposed in the housing cover; and a screw connection configured toscrew-couple the housing cover to the housing, the screw connectionincluding sawtooth thread between the housing and the housing cover;wherein the screw connection includes an external thread side includinga material having a first thermal expansion coefficient and an internalthread side including a material having a second thermal expansioncoefficient less than the first thermal expansion coefficient, andwherein a flank angle of the sawtooth thread is <0°.
 7. A reciprocatingpiston-type machine, comprising: a housing; a housing cover; a powerunit disposed in the housing and including a plurality of pistons; oneof a suction and discharge area and a forward shaft bearing disposed inthe housing cover; and a screw connection configured to screw-couple thehousing cover to the housing, the screw connection including sawtooththread between the housing and the housing cover; wherein the screwconnection includes an external thread side including a material havinga first thermal expansion coefficient and an internal thread sideincluding a material having a second thermal expansion coefficientgreater than the first thermal expansion coefficient, and wherein aflank angle of the sawtooth thread is >3°.